How does the misperception effect explain why a short-run aggregate supply curve is upward sloping? because of fixed-wage labour contracts because profit margins fall as the price level rises O because the costs of production rise as the price level rises O because people mistake changes in aggregate demand for changes in the demand for their goods relative to other goods and services If some non-price level determinant causes total spending to decrease, what will the effect on aggregate demand be? a movement upward along the curve O a movement downward along the curve a shift to the left O a shift to the right